Resumen:

Ultra-fine grained (UFG) metallic materials have been a hot topic in materials science
for the last 25 years. There is a significant body of research showing that the UFG
materials have very high mechanical strength, but their commercialisation is limited duUltra-fine grained (UFG) metallic materials have been a hot topic in materials science
for the last 25 years. There is a significant body of research showing that the UFG
materials have very high mechanical strength, but their commercialisation is limited due
to their low uni-axial tensile ductility. The main objective of this PhD thesis is to study
the bi-axial stretching formability of the UFG metallic materials. It is demonstrated that
there is a significant effect of the stress state (stress triaxiality) on mechanisms
operating during plastic deformation in the UFG commercially pure (CP) Cu and the
deformation mechanisms are determined by the stress state. The microstructure of the
UFG CP Cu can be designed in such a way so as to show very high formability, even
exceeding that of its coarse-grained counterpart. The effect of metallographic and
crystallographic texture on the bi-axial stretching formability of the UFG CP Ti has been
analysed. It is shown that the UFG CP Ti can show bi-axial stretching formability
sufficient for metalforming operations. Coarse dispersoids and fractured particles in the
Al 2024 alloy significantly limit its formability, acting as sites for the formation of cracks
leading to sample failure at the early stages of deformation. Based on the analysis of
the experimental results, a general recipe to improve formability of the UFG metallic
materials is proposed. ------------------------------------------------------------------------------------[+][-]